1. Field of the Invention
The present invention relates to a method of manufacturing a thin film magnetic head, and more particularly to a method of manufacturing a combination type thin film magnetic head constructed by stacking an inductive type writing thin film magnetic head and a magnetoresistive type reading thin film magnetic head on a substrate in an electrically insulating and magnetically isolated manner.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. In general, as a reading magnetoresistive element, an element utilizing anisotropic magnetoresistive (AMR) effect has been used so far, but there has been further developed a GMR reproducing element utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than that of the normal anisotropic magnetoresistive effect by several times. In the present specification, elements exhibiting a magnetoresistive effect such as AMR and GMR reproducing elements are termed as a magnetoresistive reproducing element or MR reproducing element. By using the AMR reproducing element, a very high surface recording density of several gigabits/inch.sup.2 has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes. A height (MR Height: MRH) of a magnetoresistive reproducing element is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. The MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface ABS. During a manufacturing process of the magnetic head, a desired MR height can be obtained by controlling an amount of polishing the ABS.
The performance of the recording magnetic head is also required to be improved in accordance with the improvement of the performance of the reproducing magnetic head. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a write gap at the air bearing surface has to be reduced to a value within a range from several microns to several sub-microns. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head. One of factors determining the performance of the inductive type thin film writing magnetic head is a throat height TH. This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible.
FIGS. 1-12 show successive steps for manufacturing a conventional standard thin film magnetic head and a plan view illustrating a completed thin film magnetic head. It should be noted that the thin film magnetic head is of a combination type in which an inductive type thin film magnetic head for writing and a reproducing thin film magnetic head including a MR element are stacked on a substrate.
First of all, as shown in FIG. 1, an insulating layer 112 consisting of alumina is deposited on a substance 111 made of, for instance AlTiC and having a thickness of about 5-10 .mu.m. Next, as shown in FIG. 2, after forming a bottom shield magnetic layer 113 which protects the MR reproduction element of the reproducing head from the influence of an external magnetic field, an alumina insulating layer 114 of thickness 100-150 nm is deposited by sputtering as shown in FIG. 3.
As illustrated in FIG. 3, a magnetoresistive layer 115 made of a material having the magnetoresistive effect and constituting the MR reproduction element is formed on the insulating layer with a thickness of several tens nano meters and is then shaped into a given pattern by the highly precise mask alignment. Then, as shown in the FIG. 4, an alumina insulating layer 116 similar to the alumina insulating layer 114 is formed, and a magnetic layer 117 made of a permalloy is formed with a film thickness of 3-4 .mu.m as shown in FIG. 5. This magnetic layer 117 has not only the function of the upper shield layer which magnetically shields the MR reproduction element together with the above described bottom shield layer 113, but also has the function of one of poles of the writing thin film magnetic head. Here, the magnetic layer 117 is called a first magnetic layer by taking into account the latter function.
Then, as shown in FIG. 6, after forming a write gap layer 118 made of a non-magnetic material such as alumina and having a thickness of about 150-300 nm on the first magnetic layer 117, an electrically insulating photoresist layer 119 is formed on the gap layer, and then a first layer thin film coil 120 made of, for instance copper is formed on the photoresist layer.
Continuously, as shown in FIG. 7, after forming an electrically insulating photoresist layer 121 on the thin film coil 120 by the highly precise mask alignment, the photoresist layer is sintered at a temperature of, for example 250.degree. C. In addition, as shown in FIG. 8, a second layer thin film coil 122 is formed on the thus flattened surface of the photoresist layer 121, and after forming a photoresist layer 123 on the second layer thin film coil 122 with the highly precise mask alignment, the photoresist layer is flattened by performing the sintering process at a temperature of, for example 250.degree. C. As described above, the reason why the photoresist layers 119, 121, and 123 are formed by the highly precise mask alignment process, is that the throat height (TH) and MR height (MRH) are defined on the basis of a position of the edges of the photoresist layers on a side of the pole portion.
Next, as shown in FIG. 9, a second magnetic layer 124 made of, for example a permalloy and having a thickness of 3-4 .mu.m is selectively formed on the gap layer 118 and photoresist layers 119, 121 and 123 in accordance with a desired pattern.
This second magnetic layer 1124 is coupled with the first magnetic layer 117 at a rear position remote from the magnetoresistive layer 115 such that the thin film coils 120, 122 pass through a closed magnetic circuit composed of the first and second magnetic layers. The second magnetic layer 124 includes a pole portion which has desired configuration and size defining a track width. Furthermore, an overcoat layer 125 made of alumina is deposited on the exposed surfaces of the second magnetic layer 124 and gap layer 118. In an actual thin film magnetic head, electric conductors and contact pads for performing the electrical connection to the thin film coils 120, 122 and MR reproduction element are formed, but they are not shown in the drawings.
In an actual manufacturing process of the combination type thin film magnetic head, the above mentioned substrate 111 is formed by a wafer, and after forming a number of thin film magnetic head units in the wafer in matrix, the wafer is divided into a plurality of bars in which a plurality of thin film magnetic head units are aligned, a side surface of a bar is polished to obtain simultaneously air bearing surfaces of said plurality of thin film magnetic heads, and finally the bar is divided into respective thin film magnetic head. That is to say, as shown in FIG. 10, a side wall 126 at which the magnetoresistive layer 115 is formed is polished to form the air bearing surface 127 which is to be opposed to a magnetic record medium. During the formation of the air bearing surface 127, the magnetoresistive layer 115 is also polished to obtain a MR reproducing element 128. In this way, the above described throat height TH and the MR height MRH are determined.
The polishing for obtaining the air bearing surface could not be conducted while the throat height TH and MR height MRH are actually monitored. Therefore, in the known technique, an electrically conductive patter (not shown in the drawing) connected to the magnetoresistive layer 115 is connected to a resistance measuring circuit, a change in resistance of the magnetoresistive layer 115 due to the decrease in a height of the magnetoresistive layer by polishing is detected as a change in a current, and an amount of polishing of the magnetoresistive layer 115 is calculated in accordance with said change in the current. That is to say, the desired MR height MRH and throat height TH are obtained by conducting the polishing such that the resistance of the MR reproducing element 128 becomes a given value.
FIGS. 10, 11 and 12 are cross sectional view, front view and plan view showing the known combination type thin film magnetic head manufactured in the manner explained above, while the overcoat layer 125 is dispensed with. In FIG. 10, the alumina insulating layers 114 and 116 are shown as a single insulating layer, and in the plan view of FIG. 12, the thin film coils 120, 122 are shown concentrically for the sake of simplicity. As shown in FIG. 10, an angle .theta. (apex angle) between a line S connecting side comers of the photoresist layers 119, 121, 123 for isolating the thin film coils 120, 122 and the upper surface of the second magnetic layer 124 is an important factor for determining the performance of the thin film magnetic head together with the above described throat height TH and MR height MRH. Moreover, as shown in the plan view of FIG. 12, the width W of a pole portion 124a of the second magnetic layer 124 is small. Since the width of the track recorded on the magnetic record medium is defined by this width W, it is necessary to narrow this width as small as possible in order to achieve a high surface recording density.
In order to improve the surface recording density of the magnetic record medium, it has been required to improve the performance of the recording head as well as the reading head. In the method of manufacturing the combination type thin film magnetic head, the control of sub-micron order using the semiconductor manufacturing technique is indispensable. A manufacturing yield of the combination type thin film magnetic head is largely dependent upon the throat height TH and apex angle .theta. of the writing inductive type thin film magnetic head and the MR height MRH of the reading magnetoresistive type thin film magnetic head.
As has been explained above with reference to FIGS. 1-12, in the known method of manufacturing the thin film magnetic head, the air bearing surface is polished while the resistance of the magnetoresistive layer 115 of the MR element is measured. However, even if the resistance becomes a given value, the throat height TH and apex angle .theta. of the writing thin film magnetic head could not be always become desired values. That is to say, during the formation of the writing thin film magnetic head, the positional reference of throat height zero position is defined by the edge of the photoresist layer 119 and the apex angle is defined by a side profile of the photoresist layers 119, 121, 123, but these photoresist layers might be deformed by the heating treatment at about 250.degree. C. during the formation of the thin film coils 120, 122, and thus the positional reference of the throat height zero position and the side profile are changed. Particularly, when the photoresist layers 119, 121, 123 have a large thickness, a deviation of its pattern becomes very large such as about 0.5 .mu.m, and therefore it is no more impossible to realize the fine throat height of the order of several microns to sub-microns in a reliable manner and the desired apex angle could not be attained. Furthermore, in case of using the thick photoresist layers, the pattern might be deviated also due to an unevenness in thickness.
For instance, in the thin film magnetic head for high frequency, the throat height is required to be not larger than 1.0 .mu.m, but due to the above mentioned large error up to 0.5 .mu.m, the throat height might deviate from a desired value during the process of polishing the air bearing surface, and thus a manufacturing cost might be increased. Moreover, since the apex angle has a very small tolerance, the apex angle is liable to be out of the tolerance.
In order to mitigate the above mentioned problem, it has been proposed to form a depressed or recessed portion in the surface of the substrate defining the positional reference of throat height zero. By forming such a recessed portion, an edge of the recessed portion can be utilized as the throat height zero position, and since the position of the edge does not shift during the manufacturing process, the above problem can be solved.
In Japanese Patent Laid-open Publication Kokai Sho 60-193114, there is described a method of forming a recessed portion in a surface of a substrate, i.e. wafer by means of a blade.
In Japanese Patent Publication 62-220512, there is described another method of forming the recessed portion, in which a mask is formed by patterning a photoresist layer, and a wet etching is carried out by using a mixture of HF+HNO.sub.3.
Furthermore, in Japanese Patent Laid-open Publication Kokai Hei 8-7225, there is described a method of forming the recessed portion, in which after forming a layer made of ceramics such as aluminum oxide and silicon oxide on a wafer surface, a mask is formed on this layer by patterning a photoresist layer, and the recessed portion is formed by a wet etching using a solution of calcium hydroxide.
Moreover, In Japanese Patent Laid-open Publication Kokai Hei 1-211311, there is described still another method of forming the recessed portion, in which after forming the photoresist mask like as the above mentioned Japanese Patent Laid-open Publication Kokai Hei 8-7225, the recessed portion is formed by an ion beam etching.
However, in the above mentioned mechanical method using the blade, it is difficult to form the recessed portion having desired depth and configuration with a precision of several microns. Moreover, a smoothness of a cut surface is extremely poor.
Moreover, in the method of forming the recessed portion by the wet etching, it is difficult to conduct the anisotropic etching, and thus a side etching might be produced within the recessed portion. Therefore, also in this method, it is difficult to obtain the recessed portion having the smooth inner wall and uniform inclination angle.
Further, in the dry etching such as the ion beam etching, an etching rate is very small, and therefore it is practically difficult to form the recessed portion having a depth not smaller than 5 .mu.m. Furthermore, debris of etched substances might be adhered to the substrate and the pattern of the recessed portion might be deviated from a desired shape. The etching speed is very low.